### FILE="Main.annotation"
# Copyright:    Public domain.
# Filename:	LATITUDE_LONGITUDE_SUBROUTINES.agc
# Purpose:      Part of the source code for Colossus build 237.
#               This is for the Command Module's (CM) Apollo Guidance
#               Computer (AGC), we believe for Apollo 8.
# Assembler:    yaYUL
# Contact:      Jim Lawton <jim DOT lawton AT gmail DOT com>
# Website:      www.ibiblio.org/apollo/index.html
# Page scans:   www.ibiblio.org/apollo/ScansForConversion/Colossus237/
# Mod history:  2011-04-13 JL	Adapted from corresponding Colossus 249 file.

## Page 1203
# SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT

# CALLING SEQUENCE

#   L-1    CALL
#   L             LAT-LONG
# SUBROUTINES USED

#  R-TO-RP,ARCTAN,SETGAMMA,SETRE
# ERASABLE INIT. REQ.

#   AXO,-AYO,AZO,TEPHEM (SET AT LAUNCH TIME)
# ALPHAV = POSITION VECTOR METERS B-29
#   MPAC-- TIME (CSECS B-28)
#  ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
#  LUNAFLAG=0 FOR EARTH,1 FOR MOON
# OUTPUT

#   LATITUDE IN LAT   (REVS. B-0)
#   LONGITUDE IN LONG   (REVS. B-0)
# ALTITUDE IN ALT METERS B-29
		BANK	30
		SETLOC	LATLONG
		BANK

		COUNT	13/LT-LG

		EBANK=	ALPHAV
LAT-LONG	STQ	SETPD
			INCORPEX
			0D
		STOVL	6D		# SAVE TIME IN 6-7D FOR R-TO-RP
			ALPHAV
		PUSH	ABVAL		# 0-5D= R FOR R-TO-RP
		STODL	ALPHAM		# ABS. VALUE OF R FOR ALT FORMULA BELOW
			ZEROVEC		# SET MPAC=0 FOR EARTH,NON-ZERO FOR MOON
		BOFF	COS		# USE COS(0) TO GET NON-ZERO IN MPAC
			LUNAFLAG	# 0=EARTH,1=MOON
			CALLRTRP
CALLRTRP	CALL
			R-TO-RP		# RP VECTOR CONVERTED FROM R B-29
		UNIT			# UNIT RP B-1
		STCALL	ALPHAV		# U2= 1/2 SINL FOR SETRE SUBR BELOW
			SETGAMMA	#  SET GAMMA=B2/A2 FOR EARTH,=1 FOR MOON
		CALL			#  SCALED B-1
			SETRE		# CALC RE METERS B-29
		DLOAD	DSQ
			ALPHAV
		PDDL	DSQ
			ALPHAV +2
## Page 1204
		DAD	SQRT
		DMP	SL1R
			GAMRP
		STODL	COSTH		# COS(LAT) B-1
			ALPHAV +4
		STCALL	SINTH		# SIN(LAT) B-1
			ARCTAN
		STODL	LAT		# LAT B0
			ALPHAV
		STODL	COSTH		# COS(LONG) B-1
			ALPHAV +2
		STCALL	SINTH		# SIN(LONG) B-1
			ARCTAN
		STODL	LONG		# LONG. REVS B-0 IN RANGE -1/2 TO 1/2
			ALPHAM
		DSU			# ALT= R-RE METERS B-29
			ERADM
		STCALL	ALT		# EXIT WITH ALT METERS B-29
			INCORPEX

## Page 1205
# SUBROUTINE TO CONVERT LAT,LONG.ALT AT GIVEN TIME TO RADIUS VECTOR
# CALLING SEQUENCE

#   L-1    CALL
#   L             LALOTORV
# SUBROUTINES USED

#  SETGAMMA,SETRE,RP-TO-R
# ERASABLE INIT. REQ.

#   AXO,AYO,AZO,TEPHEM  SET AT LAUNCH TIME
#   LAT-- LATITUDE  (REVS B0)
#   LONG-- LONGITUDE  (REVS B0)
# ALT--ALTITUDE (METERS) B-29
#   MPAC-- TIME  (CSECS B-28)
#   ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
#   LUNAFLAG=0 FOR EARTH,1 FOR MOON
# OUTPUT

# R-VECTOR IN ALPHAV (METERS B-29)
LALOTORV	STQ	SETPD		# LAT,LONG,ALT TO R VECTOR
			INCORPEX
			0D
		STCALL	6D		# 6-7D= TIME FOR RP-TO-R
			SETGAMMA	# GAMMA=B2/A2 FOR EARTH,1 FOR MOON B-1
		DLOAD	SIN		#               COS(LONG)COS(LAT) IN MPAC
			LAT		#      UNIT RP= SIN(LONG)COS(LAT)    2-3D
		DMPR	PDDL		# PD 2          GAMMA*SIN(LAT)       0-1D
			GAMRP
			LAT		#         0-1D= GAMMA*SIN(LAT) B-2
		COS	PDDL		# PD 4     2-3D=COS(LAT) B-1 TEMPORARILY
			LONG
		SIN	DMPR		# PD 2
		PDDL	COS		# PD 4    2-3D=SIN(LONG)COS(LAT) B-2
			LAT
		PDDL	COS		# PD 6     4-5D=COS(LAT) B-1 TEMPORARILY
			LONG
		DMPR	VDEF		# PD4     MPAC= COS(LONG)COS(LAT) B-2
		UNIT	PUSH		# 0-5D= UNIT RP FOR RP-TO-R SUBR.
		STCALL	ALPHAV		# ALPHAV +4= SINL FOR SETRE SUBR.
			SETRE		# RE METERS B-29
		DLOAD	BOFF		# SET MPAC=0 FOR EARTH,NON-ZERO FOR MOON
			ZEROVEC
			LUNAFLAG
			CALLRPRT
		COS			# USE COS(0) TO GET NON-ZERO IN MPAC
CALLRPRT	CALL
			RP-TO-R		# EXIT WITH UNIT R VECTOR IN MPAC
		STODL	ALPHAV
			ERADM
## Page 1206
		DAD	VXSC		# (RE + ALT)(UNIT R) METERS B-30
			ALT
			ALPHAV
		VSL1			# R METERS B-29
		STCALL	ALPHAV		# EXIT WITH R IN METERS B-29
			INCORPEX
# SUBROUTINE TO COMPUTE EARTH RADIUS

# INPUT

#   1/2 SIN LAT IN ALPHAV +4

# OUTPUT

#   EARTH RADIUS IN ERADM AND MPAC  (METERS B-29)

GETERAD		DLOAD	DSQ
			ALPHAV +4	# SIN**2(L)
		SL1	BDSU
			DP1/2		# COS**2(L)
		DMPR	BDSU
			EE
			DP1/2
		BDDV	SQRT
			B2XSC
		SR4R
		STORE	ERADM
		RVQ

# THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166,B=6356784 METERS
# B2XSC= B**2 SCALED B-51
# B2/A2= B**2/A**2 SCALED B-1
# EE=(1-B**2/A**2) SCALED B-0

B2XSC		2DEC	.0179450689	 # B**2 SCALED B-51
DP1/2		=	XUNIT
B2/A2		2DEC	.9933064884 B-1	 # GAMMA= B**2/A**2 B-1
EE		2DEC	6.6935116 E-3	 # (1-B**2/A**2) B-0
ERAD		2DEC	6373338 B-29	# PAD RADIUS

## Page 1207
# ARCTAN SUBROUTINE


# CALLING SEQUENCE

#   SIN THETA IN SINTH B-1
#   COS THETA IN COSTH B-1
#   CALL ARCTAN

# OUTPUT
#   ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2


ARCTAN		BOV
			CLROVFLW
CLROVFLW	DLOAD	DSQ
			SINTH
		PDDL	DSQ
			COSTH
		DAD
		BZE	SQRT
			ARCTANXX	# ATAN=0/0  SET THETA=0
		BDDV	BOV
			SINTH
			ATAN=90
		SR1	ASIN
		STORE	THETA
		PDDL	BMN
			COSTH
			NEGCOS
		DLOAD	RVQ
NEGCOS		DLOAD	DCOMP
		BPL	DAD
			NEGOUT
			DP1/2
ARCTANXX	STORE	THETA
		RVQ

NEGOUT		DSU	GOTO
			DP1/2
			ARCTANXX
ATAN=90		DLOAD	SIGN
			LODP1/4
			SINTH
		STORE	THETA
		RVQ

2DZERO		=	DPZERO

## Page 1208
# ..... SETGAMMA SUBROUTINE .....
# SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES

#  GAMMA = B**2/A**2 FOR EARTH (B-1)
#  GAMMA = 1 FOR MOON (B-1)

# CALLING SEQUENCE
#  L       CALL
#  L+1            SETGAMMA

# INPUT
#  LUNAFLAG=0 FOR EARTH,=1 FOR MOON

# OUTPUT
#  GAMMA IN GAMRP  (B-1)

SETGAMMA	DLOAD	BOFF		# BRANCH FOR EARTH
			B2/A2		# EARTH GAMMA
			LUNAFLAG
			SETGMEX
		SLOAD
			1B1		# MOON GAMMA
SETGMEX		STORE	GAMRP
		RVQ
GAMRP		=	8D

## Page 1209
# .....SETRE SUBROUTINE .....1
# SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)

# RE= RM FOR MOON
#  RE= RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID

# CALLING SEQUENCE
#  L       CALL
#  L+1            SETRE

# SUBROUTINES USED
#  CETERAD

# INPUT
#  ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED RE
#  ALPHAV +4= 1/2 SINL IF GETERAD IS CALLED
#  LUNAFLAG=0 FOR EARTH,=1 FOR MOON

# OUTPUT
#  ERADM= 504RM FOR MOON (METERS B-29)
#  ERADM= ERAD OR COMPUTED RE FOR EARTH (METERS B-29)

SETRE		STQ	DLOAD
			SETREX
			504RM
		BON	DLOAD		# BRANCH FOR MOON
			LUNAFLAG
			TSTRLSRM
			ERAD
		BOFF	CALL		# ERADFLAG=0 FOR FIXED RE,1 FOR COMPUTED
			ERADFLAG
			SETRXX
			GETERAD
SETRXX		STCALL	ERADM		# EXIT WITH RE OR RM METERS B-29
			SETREX
TSTRLSRM	BON	VLOAD		# ERADFLAG=0,SET R0=RLS
			ERADFLAG	#         =1     R0=RM
			SETRXX
			RLS
		ABVAL	SR2R		# SCALE FROM B-27 TO B-29
		GOTO
			SETRXX
SETREX		=	S2
504RM		2DEC	1738090 B-29	# METERS B-29 (MOON RADIUS)
